HIIT vs LISS Cardio | Which Burns More Fat?

Did the top stop spinning at the end of Inception? Should you break apart an Oreo or bite into the whole thing? Could the door have supported both Jack and Rose?! I love debating. Jenae and I took the “16 Personalities” test last month. Was I surprised that my result was The Debater? My husband sure wasn’t. So my personality is defined as the “ultimate devil’s advocate”…. sue me.

One of my favorite debates is the widely popular HIIT vs LISS discussion. Allow me to preface that while I currently perform neither, both forms of cardio are effective and beneficial for a multitude of different reasons… but the keyword is different. What might be best for improving your VO2 max might not be best for getting you “summer ready,” but more on that later. Let’s start with some basic definitions. Below is a list I’m pulling straight from my article on whether cardio is helping or hurting your weight-loss goals (link here).

High Intensity Interval Training [HIIT]:

Short bursts of all-out anaerobic work, followed by rest periods

Large fluctuations in heart rate

Creates metabolic adaptions (increases your metabolism), as long as you are reaching your anaerobic and lactate thresholds

Induces a 24 hour boost in metabolism

Taps into abdominal fat storage

Increases mitochondrial capacity (where ATP is produced and fat is burned)

Allows retention and even increases in muscle mass, as long as cardio mimics multi-joint exercises with plenty of hip flexion

Low Intensity Steady State [LISS]:

Consistent period of work at a low to moderate intensity

No fluctuations in heart rate

Creates no metabolic adaptions, and even tends to slow the metabolism

Burns calories only in the given period of cardio, as opposed to the HIIT “after-burn”

If you’re looking to lose some weight and keep it off, it is my opinion that you should look for 3 major criteria from your cardio:

1. Ability to Burn Fat

Let’s talk about something we all remember from high school: mitochondria. Everyone say it together now- mitochondria is the powerhouse of the cell. It’s also where ATP is produced and fat is oxidized (burned). We all want to be fat-burning machines, right? To make that possible, you want a LARGE mitochondrial capacity. That’s where HIIT cardio comes in and gives us superpowers- it actually increases that capacity, while zero studies show that LISS cardio does the same.

Speaking of ATP production, I’ve got two more science terms for you: anaerobic threshold (AT) and lactate threshold (LT). When you reach these thresholds, you have gotten to the level where blood lactate accumulates above resting levels, resulting in greater ATP production. More ATP produced = more fat burned. These thresholds are only possible through short bursts of anaerobic work… aka HIIT cardio.

Plain and simple, HIIT is more efficient at burning fat.

2. Ability to Keep Metabolic Rate as High as Possible

So what is this 24 hour boost in metabolism that HIIT cardio allegedly brings? This phenomenon is made possible through staying above the two thresholds mentioned above. Okay so how do you know if you’re reaching those thresholds? While you can actually get yours tested in a lab while performing anaerobic work, an easier test is whether or not you can talk during your work intervals. I wish I could tell you it’s easy to get there… but it takes work, and this is where I see major discrepancies in the fitness industry. A lot of people aren’t willing to reach maximum capacity.

Making your rest periods a priority ensures that you can perform at that maximum capacity for the next interval

Work as hard as you can for 10-30 seconds, then take 2-3 minutes (or more) to recover. Yes, it is possible that you could be at the level of fitness where you don’t need 3 minutes to recover. The test? How long does your heart rate take to go back down? I don’t know about y’all, but my heart feels like it’s exploding out of my chest well beyond the first minute of recovery.

A huge mistake I see is people performing “HIIT cardio,” and their rest intervals are less than 30 seconds?? Or even worse, their work time is larger than their rest time, such as 20 seconds of work and 10 seconds of rest. You can keep calling it HIIT, but that my friend is called tabata. Tabata is a highly effective training principle nonetheless, but it’s effectiveness lies in it’s ability to improve your VO2 max… not burn fat. Fat loss may occur, but save the tabata for that half-marathon you’ve always wanted to accomplish! If you want to get serious about metabolic adaptions and therefore fat loss, increase the rest time and shorten the work time so you can put the high in high intensity am I right?! (*crickets*)

3. Ability to Retain Muscle Mass

More muscle mass = the ability to have a higher metabolic rate. Multiple studies have shown that HIIT cardio retains muscle more efficiently than LISS cardio. HIIT cardio even has the ability to increase muscle mass!

Have you ever looked at an endurance runner and a sprinter side by side? Greater hip flexion = more muscle fibers engaged = more muscle fiber growth. I’ve heard girls say they built their booty by walking on the stair master or incline on the treadmill. While there is nothing inherently wrong with these exercises, that is not how you built a booty. HIP FLEXION. RAPID CONTRACTIONS. POWER. Those are key.

Wrapping things up, HIIT cardio is by far superior for fat loss when compared with LISS cardio. Thank you for stopping by and reading! Subscribe to our blog for fitness & nutrition posts every week:)